Re: Proposal for matching negated sets (was Re: New Public Review Issue: Proposed Update UTS #18)

From: Mike (
Date: Thu Oct 04 2007 - 22:59:51 CDT

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    > With strings in sets at all, separately from the question of how to do
    > set negation, I'm not sure how matching should work. Which choice is
    > selected if more than one is possible? Should backtracking try
    > additional choices if the first one doesn't lead to an overall match?
    > If sets don't have an implied ordering, do we need to require a POSIX
    > style longest match, which could be slow?

    In a set, I keep track of the strings by their length, so the longest
    match is always found. I don't think you want to backtrack and try a
    shorter string since the longer match is supposed to be treated as a

    > Should the set [^xyz\q{ch}] match the 'c' in "ch" ?

    I don't think so; since the \q{ch} matches "ch", the negated set does
    not match at the first position.

    > I'm half inclined to move strings, or literal clusters, into section 3,
    > then move the entire section 3 of UTS-18 into a separate document for
    > interesting, but not fully worked out, ideas.

    This seems like a good idea.


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